The present invention relates to the preparation of packing materials and the like, and more particularly to an improved cutting assembly for determining the proper length of a packing and severing the same.
In many types of mechanisms it is necessary to provide a seal about an axle, rod, or other shaft-like member. Such seals are commonly held in place by appropriate means surrounding the element, such as glands, stuffing boxes and the like. The seal is constituted by a length of packing material, and is commonly used to prevent the ingress or escape of fluids such as water or hydraulic oil, or to prevent foreign materials such as particulate matter from entering a mechanism. The packing is commonly of a resilient material which must be resistant to attack from the various materials with which it comes in contact. At one time such packings were formed of various fibrous ropes or yarns impregnated with suitable lubricants, binders and other materials, or of strands of metal, such as lead. The packing was simply wrapped about the shaft element and then axially compressed, the compression serving to squeeze the packing tightly about the shaft thereby providing a fluid-tight seal. With modern machinery endless packing rings are often utilized; and many synthetic materials have been developed which exhibit superior sealing characteristics and are moreover highly resistant to the various materials which they encounter.
In some cases, however, it is impossible or inconvenient to use an endless packing ring. The shaft element may, for instance, have enlarged ends or the ends may otherwise be inaccessible so that an endless ring cannot be slipped over them; or, it may be economically impractical to manufacture and store all of the various types and sizes of endless ring packings which could conceivably be required.
For this reason it is commonplace to form ring packings for shafts and the like from a length of stock material by cutting the material to length by various means such as knives, shears, saws and the like. Over the years various types of apparatus have been devised to facilitate the task of calculating and measuring the precise length of the packing which is required. Examples of such devices are disclosed in U.S. Pat. No. 1,745,815-Schoepfle and U.S. Pat. No. 3,487,773-Meier. According to such prior art approaches, the inside and outside diameters of the requisite packing ring were determined and averaged, and this figure used to determine the length of the packing strip which was required. As will be readily recognized, determining the precise length of the packing is critical to the satisfactory operation of the same since too long a packing will be compressed too much in the stuffing box or gland and may engage the moving shaft member too tightly. On the other hand too short a packing will leave an open gap between the confronting ends, which defeats the purpose of the packing by providing an opening adjacent the shaft member.
Calculation and measurement of a packing of the proper length is made difficult by the fact that the ends of the packing are preferably cut on a bias and also since the packing, having a rather substantial width, exhibits a perceptible change in its length as it is bent into a curve. More specifically, when bent the radially inner portions of the packing tend to be compressed, while the radially outermost elements are stretched somewhat. In order to determine the proper length of such packing, a trial-and-error method is often used; or a mandrel or ring of the same diameter as the shaft member is prepared, and the packing wound about the periphery of the ring so that the precise required length can be determined. The deficiencies of this approach are apparent, inasmuch as a packing supplier must prepare and keep on hand a forming ring for each shaft size for which a packing may be required. In addition to the physical problem presented by preparation, handling and storage of these devices, an inordinate amount of time is required for selecting and readying each element for the cutting of a packing.
To further complicate matters, certain of the more recently developed types of packing are formed of elastomeric materials which are extruded and coiled during their manufacture. These packing materials are then transported to users in coiled form. Such preformed packing material has a fixed, standard radius of curvature, so that its effective length changes as it is stretched about a forming element whose radius is either larger or smaller than the preformed radius of the packing material. The resulting distortions in the packing further complicate the task of determining the proper length of packing material for a given shaft size. Either the distortion must be taken into consideration when cutting the packings to length or else individual forming rings must be used, as described above.
From the foregoing, it will be understood that it would be highly desirable to provide a single, compact apparatus for determining the proper length of a segment of packing material and for cutting the packing to the precise length without the need for a multiplicity of forming rings.
It is therefore an object of the present invention to provide an improved apparatus for measuring and cutting packing materials.
Another object of the invention is to provide means for facilitating the measuring and cutting of permanently coiled elastomeric packing materials.
Yet another object is to furnish a single packing forming means which accommodates packings for shaft elements of disparate diameters.